1. Field of the Invention
The present invention relates to a new and improved filter design. More particularly, the present invention relates to a filter comprised of at least two concentric annular filter elements which are folded in helical pleats of opposite directions so that the inside pleats of the outer filter element touch the outer pleats of the inner filter element, supporting each other and forming channels between them through which filtered material may pass as it exits the filter.
2. The Prior Art
Preliminary searches were conducted on the invention disclosed herein, and the following listed patents were uncovered in the searches:
______________________________________ Patent No. Inventor Issue Date ______________________________________ 628,534 Haefner July 11, 1899 2,387,368 Vokes October 23, 1945 3,204,771 Baldwin September 7, 1965 3,211,292 Bull October 12, 1965 3,361,260 Buckman January 2, 1968 3,370,708 Hultgren February 27, 1968 3,420,377 Vandersip January 7, 1969 3,467,256 Humbert September 16, 1969 3,988,244 Brooks October 26, 1976 4,036,758 Combest July 19, 1977 4,317,727 Meissner March 2, 1982 4,507,200 Meissner March 26, 1985 4,537,681 Argiropoulos August 27, 1985 ______________________________________
One type of filter in common use employs a filter cartridge comprised of inner and outer concentric annular filter elements separated by an annular region. The filter elements used are normally made of filter paper which has been folded in an axial orientation. The filter cartridge is mounted in a housing having an inlet communicating with the outer surface of the outer filter element and the inner surface of the inner filter element and an outlet communicating with the annular region between the two filter elements.
Material to be filtered flows into the filter through the inlet and then flow radially inward through the outer filter element and radially outward through the inner filter element to the annular region between the filter elements and then flows axially through the annular region to the outlet.
A problem of the described filer cartridge is the tendency of its filter elements to collapse toward the annular region due to the opposing forces exerted thereon by the differential pressures between the inside and outside surfaces of the filter elements. The axially folded pleats of the collapsing filter element tend to enmesh with the axially folded pleats of the other filter element, restricting flow to the outlet and reducing the useful life of the filter elements.
Various devices and materials have been employed for supporting the filter elements and providing a channel between the filter elements, but addition of these devices or materials adds to the total cost of producing a filter.
An example of a typical prior art solution to this problem is disclosed in U.S. Pat. No. 3,988,244 which teaches a way to prevent collapse of the filter elements by positioning a "fluid carrier element" between the filter elements. By positioning the "fluid carrier element" between the inner surface of the outside filter element and the outer surface of the inside filter element, the device acts to cancel the forces exerted on the filter elements by the pressure differential. However, addition of the "fluid carrier element" increases the total cost of the filter.
U.S. Pat. No. 3,361,260 teaches a method of impressing spacer dimples into axially folded filter elements to hold them in place without the addition of other devices or materials. However, spacer dimples do not provide sufficient support to the filter elements.
The remaining patents listed above are not considered sufficiently pertinent as to require any comment.
The present invention is superior to the prior art in that it allows a shorter pleat height in the filter elements with increased surface area and increased collapse resistance. The invention's helically pleated filter elements are superior to those of the prior art in that they have uniform spacing between the pleats and are self-supporting which avoids the extra cost of filter supports in the manufacture of the filter cartridge.